The present invention relates to an electrophotographic type printer using toners, and more particularly, to such printer capable of economizing toner consumption amount.
In a conventional electrophotographic type printer such as a laser printer, laser beam is irradiated for exposure to provide a latent image on a photosensitive drum, and toner are electrostatically attracted onto the drum. In this case, consumption amount of toner for use in development will greatly influence to the running cost of the printer. In this connection, as described in a Japanese Patent Application Kokai No. Hei 2-144574, there has been provided a printer provided with a toner consumption economizing mode for reducing running cost so as to cut down the toner consumption by thinning out dots to be printed in accordance with a predetermined rule, if the toner consumption economizing mode is selected.
However, in the printing device of the JP'574 4 publication, printing to a sheet is performed after the thinning-out process of the dot data if the toner economizing mode is selected. As a result, a fine character or line to be printed on the sheet may not be printed onto the sheet to degrade the printing quality.
A Japanese Patent Application Kokai No. Hei 1-133075 discloses a laser printer having two laser diode drive sources for ordinary toner consumption mode and for toner economizing mode. If the toner economizing mode is selected, the laser diode drive source is switched to reduce the laser diode driving current so as to reduce luminous intensity of the laser diode, to thereby reduce a developing area or width per one dot of the laser beam, to thus restrain the toner consumption amount.
In the laser printer of the JP'075 publication, laser diode driving current is controlled in an analog manner by switching the laser diode drive sources from one to another, and therefore, a great numbers of the laser diode driving sources are required if multi-stage control is intended. As a result, production cost may be increased and fine control may become difficult.